Electromechanical reverberation delay device



United States Patent 2 Claims ABSTRACT OF THE DISCLOSURE Reverberation device for producing delayed decaying electrical signals including a pair of vibration transmitting heilcal springs each having one end connected to an electro-mechanical transducer and the other end connected to a reflective suspension. Three links are provided interconnecting the springs, which are spaced at intervals between the middle of the springs and the ends connected to the reflective suspensions for holding the springs in spaced relation and for coupling vibrations between the strings to provide discontinuous paths between the transducers. The links prevent physical engagement of the springs when subjected to severe external vibration and shock.

"This invention relates to devices for producing delayed decaying electrical signals, and more particularly to a reverberation device which may be used in connection with sound reproduction apparatus for electrically simulating the acoustic conditions of a large room. Specifically, this invention relates to a reverberation device of the type shown and described in the co-pending application of Hugo W. Schafft, Ser. No. 324,638, filed Nov. 19, 1963,

now Patent No. 3,281,724, and assigned to the assignee of the present invention.

It has been proposed to provide a reverberation device, for producing delayed signals of decaying amplitude, comprised of a pair of helical springs each having a suspended end and an opposite end attached to a transducer. The two springs are coupled by a link intermediate the ends thereof to provide primary and secondary reflective paths. Such a device effectively simulates the sound conditions present in a large hall, auditorium or room. The concert hall effect thus attained achieves a subjective enlargement of the room or enclosure in which the listener is located.

It has been found that certain difficulties may attend the manufacture of devices in accordance with this construction. Precise delay and decay time considerations necessitate the placement of the link at a precise predetermined place along the springs, necessitating that the springs be of an exact predetermined number of turns. It has also been found that the springs may come in contact with each other in the presence of excessive exterior shock and vibration to produce excessive audio noise in the speaker of the system in which the device is used.

Accordingly, it is an object of this invention to produce a reverberation device wherein the spring tolerance is less severe, to thereby facilitate production of the device.

Another object of the invention is to provide a reverberation device which is very reliable in operation, and which provides realistic reverberation eflfects.

A further object of the invention is to provide an improved reverberation device which is constructed to inhibit contact between the springs due to excessive vibration.

A feature of the invention is the provision of a reverberation device having a pair of parallel springs, one end of each spring being connected to a transducer and the other end being suspended, and of a plurality of links spaced at predetermined intervals along the springs, connected to the springs and coupling vibrations therebetween. Three links may be provided, which are placed between the middle and the suspended ends of the springs.

In the drawing:

FIG. 1 is a top plan view of a reverberation device constructed in accordance with the invention;

FIG. 2 is a sectional view taken along the line 2-2 of FIG. 1;

FIG. 3 is a graph of the frequency response characteristics for a device of the type shown in FIG. 1 but having only a single connecting link; and

FIG. 4 is a graph of the frequency response characteristics for the device of FIG. 1 as shown.

The invention provides an effective and reliable device for producing delayed decaying electrical signals. A pair of vibration transmitting helical springs each has one end coupled to a fixed suspension. The opposite ends of the springs are connected to input and output transducers, respectively, producing torsional motion from electrical signals and electrical signals from torsional motion. A plurality of links are spaced at predetermined intervals along the springs intermediate the ends thereof and couple torsional vibrations therebetween to provide a plurality of paths for torsional virations fro-m the input transducer to the output transducer. Three links may be provided which are connected to the springs between the middle and the suspended ends thereof.

Referring more particularly to FIG. 1, a reverberation device constructed in accordance with the invention is shown. The unit is carried on a mounting plate 11 which, in turn, is attached in a housing 12 by means of rubber dampers 13 fixed to projections 14 of plate 11. A pair of transducers 16 and 17 are mounted at one end of the plate 11. Details of the transducers and their mounting are described more completely in the co-pending Schafft application, supra. Transducers 16 and 17 are substantially identical and each may serve as either the input transducer or the output transducer for the reverberation device. In FIG. 1, transducer 16 is the input or driving transducer, whereas transducer 17 is the pick-up or output transducer.

A pair of helical delay springs 20 and 21 are coupled at one end to transducers 16 and 17, respectively. Transducer 17 imparts a torsional vibration to spring 20 which is transmitted to spring 21 and received by transducer 17. The springs 20 and 21 are wound in opposite directions. This is desired because any helix, when expanded or retracted, will produce torsional motion and hence springs 20 and 21 are susceptible to producing a torsional motion by strong shock from outside of the reverberation unit. As the springs are oppositely wound, the effect of such outside vibrations is virtually cancelled out.

The ends of the springs 20 and 21 opposite the transducers are secured to fixed suspensions on plate 11. Spring 20 is provided with a hook 22, and a length of string 23 (preferably of Dacron or some other similar durable material) is knotted to the hook 22, such as by a girth hitch. A lead terminal 24 is mounted in an upwardly extending flanged end 25 of plate 11, and string 23 is drawn through a slot in terminal 24 and secured therein. The result of such a suspension is effectively equivalent to an open circuit and will act to reflect substantially all vibrations exactly in phase.

Spring 21 has hook 28 at the end thereof, which is secured in a notch 29 in an upwardly extending flange portion 30 of plate 11. Accordingly, this end of spring 21 is rigidly secured to the mass of the plate and is effectively equivalent to a short circuit. At this end of spring 21, substantially all the vibrations will be reflected with a phase reversal, that is, out of phase with the incident vibrations.

In the Schaflt application, supra, a link 33 is used to couple vibrations between springs and 21 at respective points intermediate the mid points and the suspended ends of the springs. The link includes a pair of clip portions 34 and 35 (see FIG. 2) each of which clips over the top part of a coil of one of springs 21 and 20 respectively. The clips 34 and 35 extend downwardly from opposite ends and opposite sides of the flexible cross bar 36. Because clips 34 and 35 are on opposite sides of cross bar 36, the coils of springs 21 and 20 to which they are clipped are at different distances from the transducers. This helps distribute the standing wave pattern for even frequency response and also breaks up the path lengths of travel for reflective signals for even reverberation.

In order to achieve the desired reverberation time, that is, delay and decay time, it has been found necessary to provide accurate placement of the link 33, if link 33 isthe only coupling link. For accurate placement it is necessary that each spring have the same number of turns. A slight misplacement of the link, or a more loose spring tolerance affects not only the decay and delay time but the shape of the frequency response curve of the device as well.

In accordance with the invention, a pair of further links 41 and 42, similar in construction to link 33, are spaced at intervals between link 33 and the suspended ends of springs 20 and 21. This increases the number of primary vibrational paths between the transducers 16 and 17 and provides more peaks for the frequency response curve. This result may be seen by comparing FIGURES 3 and 4. FIG. 3 is a graph of the frequency response of a device of the type shown in FIG. 1 but having only link 33 between the two springs. It will be seen from FIG. 4 that, with the addition of the two extra links 41 and 42, the response peaks which indicate the reverberation are more closely spaced, and the holes or substantial excursions of the response curve are not wide and deep in FIG. 4 as they are in FIG. 3. This means that the overall response is smoother and the reverberation effect is more realistic than in the case utilizing a single link. Furthermore, because more links are utilized and a greater spring tolerance can be accepted, the cost of the springs is reduced.

Certain conditions of use for such reverberation devices may subject the device to excessive exterior vibration and shock. For example, when such a device is mounted in an automobile, the automobile will vibrate due to variations in road surface and engine vibration and will transmit such vibrations to the reverberation device. Exterior shock mounting may be provided for the device to cushion it from such outside vibrations. Nevertheless, when such outside vibrations become excessive, the springs 20 and 21 may come in contact with each other and produce a loud noise which is heard in the speaker. The addition of links 41 and 42 with link 33 provides a more secure separation of the springs and greatly reduces the likelihood that the springs will contact each other during excessive vibrations. In addition, if one link fractures for any reason, the unit will still be workable and the decrease in quality will not be particularly noticeable. Thus, the additional links improve the total reliability of the reverberation device.

It may therefore be seen that the invention provides an improved reverberation device wherein production costs are decreased, quality is increased, reliability is improved and danger of the transmission springs contacting each other is substantially reduced.

We claim:

1. A device for producing delayed decaying electrical signals including in combination, input and output transducers for respectively producing mechanical motion from electrical signals and electrical signals from mechanical motion, a pair of vibration transmitting helical springs of substantially equal length, each having an end coupled to a respective one of said transducers, first reflective means freely suspending the other end of one of said springs to reflect vibrations in phase, second reflective means rigidly suspending the other end of the other of said springs to reflect vibrations out of phase, and a plurality of links intermediate the middle and the suspended ends of said helical springs and spaced from each other at intervals along said springs, said links holding said springs in spaced relation to prevent contact therebetween in the presence of external shocks, and coupling vibrations between said springs to provide paths for vibrations from said input transducer to said output transducer, with said reflective means providing a plurality of secondary paths for vibrations.

2 A device for producing delayed decaying electrical signals including in combination, input and output transducers for respectively producing mechanical motion from electrical signals and electrical signals from mechanical motion, a pair of vibration transmitting helical springs of substantially equal length, each having an end coupled to a respective one of said transducers, first and second refiective means suspending the other ends of said springs, and first, second and third links intermediate the middle and the suspended ends of said helical springs and spaced from each other at intervals along said springs, said links holding said springs in spaced relation in the presence of external shocks and coupling vibrations between said springs to provide paths for vibrations from said input transducer to said output transducer, with said reflective means providing a plurality of secondary paths for vibrations.

References Cited UNITED STATES PATENTS 2/1967 Schafft 33330 US. Cl. X.R. 

